Work items child widget: Migrate to crud

What does this MR do and why?

Migrates work items widgets to the shared widget component and removes it's own widget wrapper component.

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Go to an work item, e.g. Objective

Related to #452231 (closed), #476988, !161791 (diffs)

app/assets/javascripts/vue_shared/components/crud_component.vue

 <script>
-import { GlAlert, GlButton, GlIcon, GlLoadingIcon, GlLink, GlTooltipDirective } from '@gitlab/ui';
+import { GlButton, GlIcon, GlLoadingIcon, GlLink, GlTooltipDirective } from '@gitlab/ui';
 import { __ } from '~/locale';
 
 export default {
   components: {
-    GlAlert,
     GlButton,
     GlIcon,
     GlLoadingIcon,
@@ -69,11 +68,6 @@ export default {
       required: false,
       default: null,
     },
-    error: {
-      type: String,
-      required: false,
-      default: '',
-    },
   },
   data() {
     return {
@@ -221,9 +215,6 @@ export default {
       data-testid="crud-body"
     >
       <gl-loading-icon v-if="isLoading" size="sm" data-testid="crud-loading" />
-      <gl-alert v-else-if="error" variant="danger" @dismiss="$emit('dismissAlert')">
-        {{ error }}
-      </gl-alert>
       <span v-else-if="$scopedSlots.empty" class="gl-text-subtle" data-testid="crud-empty">
         <slot name="empty"></slot>
       </span>